An array of individually-addressable, movable, micro-machined mirrors can be used in optical communications networks to route or switch optical signals, e.g., optical cross connect, etc. Each mirror in the array is supported over a group of electrodes in such a way that the mirrors are free to move, e.g., rotate about an axis, etc., when actuated, such as by applying a voltage across a mirror and one or more of the underlying electrodes. By varying the amount that a mirror tilts, or the direction in which it tilts, or both, an optical signal that is incident on the mirror can be directed to a desired location, such as a particular optical fiber.
Some newer mirror arrays have mirrors that are rotatable about two perpendicular axes of rotation, e.g., as is described in U.S. Pat. No. 6,201,631, which is incorporated by reference herein.
It is desirable to provide a high density of optical transfer for communications applications. In particular, in some applications, e.g., de-multiplexing, etc., the mirrors must be very tightly spaced (about 1 to 2 microns) to enable flat pass bands with high spectral efficiency. Gimbaled mirrors, as exemplified by those described in U.S. Pat. No. 6,201,631, are not suitable for such applications because the gimbals present a limitation as to how close adjacent mirrors can be to one another. In particular, there must be a gap between adjacent mirrors that is at least twice the width of a gimbal. In fact, the minimum gap is somewhat larger than this, since the minimum gap must also take into account the gap between the mirror and the gimbal and the gap between the gimbal and the support. Furthermore, some minimum separation distance must be provided between adjacent gimbals to maintain the integrity of the substrate layer to which the gimbals are attached.
It is possible to fabricate gimbaled mirrors that are somewhat smaller than the exemplary structure disclosed in the '631 patent. Nevertheless, with the structure of prior-art gimbaled mirrors, it is not currently possible to achieve a mirror spacing of less than about 15 to 20 microns between prior-art gimbaled mirrors. Consequently, prior-art gimbaled-mirror arrays are not suitable for use in applications that require very close perimeter-to-perimeter spacing, e.g., about 15 microns or less between adjacent mirrors in a mirror array.